<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>

    // let a= 20
    // function fu(){
    //   let a =30
    // }
    // fu()
    // console.log(a)
    
    let a =1 
    function fn1(){
      let a = 2 
      let b ='22'
      fu2 ()
      function fu2(){
        let a = 3
        fu3 ()
        function fn3(){
          let a = 4 
          console.log (a)
          console.log (b)
        }
      }
    }
    fn1 ()
  </script>
</body>
</html>